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Genetic Algorithms for Positron Lifetime Data

100%
Karbowski A., Fisz J., Karwasz G., Kansy J., Brusa R.
Acta Physica Polonica A
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2008
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vol. 113
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issue 5
1365-1372
EN
Recently, genetic algorithms have been applied for ultrafast optical spectrometry in systems with several convoluted lifetimes. We apply these algorithms and compare the results with POSFIT (by Kirkegaard and Eldrup) and LT programme (by Kansy). The analysis was applied to three types of samples: molybdenum monocrystals, Czochralski-grown silicon with oxygen precipitates, Si with under-surface cavities obtained by He + H ion co- implantation. In all three tests, the genetic algorithm performs very well, in particular for short lifetimes. Further developments to model the resolution function in genetic algorithms are needed.
2
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Positronium Formation in Organic Liquids

100%
Karbowski A., Fedus K., Służewski K., Bruzdowska J., Karwasz G.
Acta Physica Polonica A
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2017
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vol. 132
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issue 5
1466-1469
EN
This paper reports on the results of positron annihilation lifetime measurements of three organic liquids: benzene (C₆H₆), cyclohexane (C₆H₁₂), and methanol (CH₃OH). The lifetime spectra are acquired at different temperatures for non-degassed, degassed, and oxygen-saturated samples, at temperatures between 5°C and 25°C. The spectra are analyzed using a standard three-exponential model. The influence of oxygen on each lifetime and intensity component is discussed.
3
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Positron-Annihilation, Structural and Optical Studies on Properties of Nanostructured ZrO_2, ZnO, Bi_2O_3 and ZnO-Bi_2O_3

86%
Fidelus J., Karbowski A., Grabis J., Jusza A., Piramidowicz R., Brusa R., Karwasz G.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6A
A-66-A-68
EN
Nanostructured oxides, like ZrO_2, on ZnO and Bi_2O_3 show interesting electronic and photovoltaic properties. Pressed and annealed samples were obtained from nanopowders grown in hydrothermal or plasma processes. Positron annihilation (the Doppler broadening depth-resolved, positron lifetime) techniques were used to trace structural changes in samples after annealing. Photoluminescence spectra of all investigated samples show broad-band emission in the visible, with intensity depending on annealing temperature. The change in nanoporosity and positron lifetimes correlate well with changes in photoluminescence properties. The nature of broad photoluminescence bands is to be understood; further positron studies via the Doppler coincidence method would help in identifying the nature of defects in these samples.
4
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Depth Profiling of Defects in He Implanted SiO_2

86%
Mariazzi S., Toniutti L., Brusa R., Duarte Naia M., Karbowski A., Karwasz G.
|
EN
Thin layer of SiO_2 thermally grown on p-type Si was implanted with He^+ ions at 30 keV with a dose of 5×10^{15} ions/cm^2. SiO_2/Si samples were depth profiled by Doppler broadening positron annihilation spectroscopy to identify induced defects in the silicon oxide, at the interface and in the Si substrate. In one sample the silicon dioxide layer was removed by etching after implantation. It is shown that removing the silicon dioxide layer some more information about defects into the substrate can be found.
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